Optical transmission device and method for driving laser diode

Abstract

An optical transmission device obtains driving control data corresponding to a temperature detected by a temperature detection circuit ( 112 ) from memory means ( 173 ), controls a driving current to be supplied to a laser diode ( 100 ) based on the driving control data, and measures a driving current to be actually supplied to the laser diode whose emission power is held constant by an automatic optical output control circuit ( 115, 113 ). Further, when the difference between the measured driving current and a driving current determined by the driving control data corresponding to the detected temperature at that time exceeds an allowable range, the optical transmission device updates the driving control data. Upon determination of the deterioration of the laser diode, the progress of the deterioration of the laser diode is determined based on the difference between a driving current defined by driving control data corresponding to a newly measured temperature and an actual driving current formed by automatic optical output control. Therefore, a distinction between whether an increase in driving current due to the automatic optical output control results from the deterioration of the laser diode and whether it results from a variation in ambient temperature is reliably made.

What is claimed is:  
     
       1. An optical transmission device, comprising: 
       a laser diode;  
       a current supply circuit for supplying a bias current and a modulating current superimposed on the bias current to said laser diode as driving currents;  
       an automatic optical output control circuit for supplementing the shortage of the driving currents so that emission power of said laser diode is held constant;  
       a temperature detection circuit for detecting an ambient temperature of said laser diode;  
       memory means for storing driving control data for determining a modulating current and a bias current necessary to obtain predetermined emission power therein for each predetermined temperature; and  
       control means for obtaining driving control data corresponding to the temperature detected by said temperature detection circuit from said memory means, controlling each driving current, to be supplied from said current supply circuit to said laser diode, based on the obtained driving control data, measuring each driving current actually supplied to said laser diode whose emission power is held constant by said automatic optical output control circuit, detecting whether the difference between the measured driving current and a driving current determined according to the driving control data corresponding to the detected temperature at that time exceeds an allowable range, and updating the driving control data related to the temperature, on said memory means when said difference exceeds the allowable range so that the difference between the driving currents is defined as each of increases in bias current and modulating current.  
     
     
       2. The optical transmission device according to claim  1 , wherein said driving control data comprises initial data for initially determining the bias current and the modulating current for each predetermined temperature and correction data subsequently added to the initial data, and said correction data is data for defining the difference between the driving currents as each of the increases in bias current and modulating current. 
     
     
       3. The optical transmission device according to claim  2 , wherein said control means allows data about the difference between the driving currents and a value obtained by increasing the difference between the driving currents by a factor of a constant ratio smaller than 1 to be included in said correction data as data about an increase in bias current, determines a bias current by the sum of the initial bias current data included in the initial data and the data about the increase in bias current included in the correction data when the driving current for said laser diode is determined based on the initial data and the correction data, and adds the initial modulating current data included in the initial data to the difference between the data about the difference between the driving currents and the data about the increase in bias current respectively included in said correction data to thereby determine a modulating current. 
     
     
       4. The optical transmission device according to claim  3 , wherein said control means includes a central processing unit and a program memory storing an operating program thereof therein, and said memory means is an electrically programmable non-volatile semiconductor memory accessible by said central processing unit. 
     
     
       5. The optical transmission device according to claim  1 , further including a cooling device capable of selectively cooling said laser diode, and wherein said control means allows said cooling device to lower an ambient temperature of said laser diode by a predetermined temperature each time the difference between the driving currents reaches a predetermined value with respect to the driving currents defined by the driving control data.